A combine harvester is a machine that is used to harvest grain crops. The objective is to complete several processes, which traditionally were distinct, in one pass of the machine over a particular part of the field. Among the grain crops that may be harvested with a combine are wheat, oats, rye, barley, corn, soybeans, flax or linseed, and others. The waste (e.g., material other than grain (MOG)) discharged on the field includes the remaining dried stems and leaves of the crop which may be, for example, chopped and spread on the field as residue or baled for feed and bedding for livestock.
A combine harvester cuts crop using a wide cutting header. The cut crop may be picked up and fed into the threshing and separating mechanism of the combine, typically consisting of a rotating threshing rotor or cylinder to which grooved steel bars commonly referred to as rasp bars or threshing elements may be bolted. These rasp bars thresh and aid in separating the grains from the MOG through the action of the drum against the concaves, i.e., shaped “half drum,” that may also be fitted with steel bars and a meshed grill, through which grain, chaff and smaller debris may fall, whereas the straw, being too big or long, is carried through to the outlet. The chaff, straw, and other undesired material (MOG) are returned to the field via a spreader mechanism.
In an axial flow combine, this threshing and separating system serves a primary separation function. The harvested crop is threshed and separated as it is conveyed between a longitudinally arranged rotor and the inner surface of a cylindrical chamber, the upper portion or top 180 degrees of the cylindrical chamber comprising a cage and the lower portion or bottom 180 degrees of the cylindrical chamber comprising threshing and separating concaves. The cut crop material, or crop mat, spirals and is conveyed along a helical path within the chamber until substantially only larger residue remains. When the residue reaches the end of the threshing drum, it is expelled out of the rear of the combine. Meanwhile, the grain, chaff, and other small debris fall through the concaves and grates onto a cleaning device or shoe. The grain still needs to be further separated from the chaff by way of a winnowing process.
Due to physical obstruction by the straw in the threshing chamber and because the rotation (e.g., angular velocity) of the crop mat around the rotor generally decreases from the center of the chamber (closer to the rotor) to the edges of the chamber (radially outward of the rotor), it becomes difficult to accelerate the grain radially outward through the crop mat to be separated out of perforations of the threshing chamber. By varying the clearance between the rotor and the threshing chamber, however, the crop mat may be compressed (pinched) to increase its angular velocity and then released to a less dense crop mat, allowing the grain to move more freely to the outside of the threshing chamber at the increased velocity to be separated out of the perforations of the threshing chamber.
U.S. Pat. No. 5,334,093, which is incorporated herein for its teachings on threshing chambers, has attempted to address the difficulty of accelerating the grain radially outward through the crop mat by a threshing chamber having a rotor which is off-set from the center of the threshing chamber toward the lower portion or bottom 180 degrees of the cylindrical chamber so that rotor and threshing chamber are non-concentric. The inventors have discovered a number of shortcomings, however, with conventional approach described in U.S. Pat. No. 5,334,093. For example, the crop mat is compressed during a counter-clockwise rotation along the bottom 180 degrees of the threshing chamber and expands during rotation along the top 180 degrees of the threshing chamber. The crop mat slows as it expands and continues to slow as it rotates along the entire top 180 degrees of the threshing chamber, which may undesirably cause the crop mat to ball-up or accumulate. When the crop mat is again compressed as it starts to rotate along the bottom 180 degrees of the threshing chamber, the crop mat now includes a stagnant clogged ball of material, making it difficult to accelerate the grain radially outward through clogged ball of material to be separated out of perforations of the threshing chamber.